Material handler with center of gravity monitoring system

ABSTRACT

A material handler that includes a frame, first and second front wheels, first and second rear wheels, and a control system. The front and rear wheels define a generally horizontal plane. The control system determines the center of gravity of the material handler and displays the location of the center of gravity of the material handler within the plane.

FIELD OF THE INVENTION

[0001] The invention relates to material handlers, and more particularlyto material handlers with telescoping booms.

BACKGROUND OF THE INVENTION

[0002] Material handlers include a frame, a front axle, a rear axle, andfront and rear wheels. Typically, the front axle is either fixedrelative to the frame or pivotal about a horizontal axis that extendscentrally along the length of the frame. The rear axle is pivotallycoupled to the rear end of the frame. The rear axle is allowed to freelypivot about the horizontal axis and thereby tilt in response to changesin ground contours in order to provide the vehicle with increasedcomfort and stability. However, under various loading conditions, thefreely pivoting rear axle may cause the material handler to become lessstable. As a result, some material handlers include rear axle stabilizersystems that have one or more lockable cylinders connected to a vehiclehydraulic system and positioned between the frame and the rear axle. Thecylinders are generally open to allow the cylinder and the rear axle tomove freely. The cylinders are also lockable to rigidly fix the positionof the rear axle relative to the frame.

[0003] Material handlers also include telescoping booms which are usedto lift and transport loads. A typical telescoping boom includes arearward or lower end that is coupled to a back end of the frame and aforward or upper end that extends toward a front end of the frame. Thetelescoping boom is extendable between a retracted position and anextended position and pivotable between a lowered position and a raisedposition. The telescoping boom is typically equipped with a fork that isinsertable underneath a pallet in order to raise a load that is stackedon top of the pallet and move it to another position. The load is movedrelative to the material handler and therefore it is possible to locatethe load into a position that will cause the material handler to becomeunbalanced and, in extreme circumstances, cause the material handler totip over.

[0004] In order to alert the operator to a potential unbalancedcondition, some material handlers include a tip over warning system toalert a vehicle operator of the amount of longitudinal weight shift fromrear to front of the vehicle. One or more strain gauges are located onthe rear axle to sense the vehicle weight supported by the axle. Thesignals from the strain gauges are used to determine the remainingweight on the rear axle of the vehicle. The system activates a warninglamp or buzzer that indicates to the operator that a longitudinal tipover may soon occur.

[0005] Other material handlers, especially cranes, include systems thatmeasure the carried load and calculate the center of gravity of themachine and load by measuring the machine geometry. Typically, thesesystems measure the angle, length, and orientation of the boom. For themethod to work properly, the machine must be level and stationary. Thesesystems activate warning alarms to warn the operator that the vehicle ispotentially unstable.

SUMMARY OF THE INVENTION

[0006] The center of gravity monitoring system of the present inventionimproves productivity by identifying when a material handler isoperating at a stable loading condition and by accurately predictingwhen the material handler is operating close to an unstable loadingcondition based on the relative loads applied to each of the frontwheels and rear wheels. The center of gravity monitoring system alsoincludes a control system that enhances productivity by not allowingmachine functions that would cause the material handler to be positionedin a more unstable loading condition. The center of gravity monitoringsystem also increases the overall efficiency of an operator and thematerial handler by eliminating the need for the operator to flipthrough manual load charts to determine the stability of a loadingcondition and by providing the operator with a display that is based onautomatically sensed parameters such as the loading applied to eachwheel.

[0007] The present invention is directed to a material handler thatincludes a frame, first and second front wheels, first and second rearwheels, and a control system. The front and rear wheels define agenerally horizontal plane. The control system determines the center ofgravity of the material handler and displays the location of the centerof gravity of the material handler within a virtual plane that isrepresentative of the plane defined by the wheels.

[0008] The present invention is also directed to a method of monitoringthe center of gravity of a material handler. The method includes sensingthe center of gravity and displaying the location of the center ofgravity of the material handler within virtual plane that isrepresentative of a plane that is defined by front and rear wheels.

[0009] Other features and advantages of the invention will becomeapparent to those skilled in the art upon review of the followingdetailed description, claims, and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a perspective view of a material handler embodying thepresent invention.

[0011]FIG. 2 is a top view illustrating a front axle of the materialhandler shown in FIG. 1.

[0012]FIG. 3 is a front view illustrating the front axle shown in FIG.2.

[0013]FIG. 4 is a top view illustrating a rear axle of the materialhandler shown in FIG. 1.

[0014]FIG. 5 is a front view illustrating the rear axle shown in FIG. 4.

[0015]FIG. 6 is a schematic view illustrating a control system of thematerial handler shown in FIG. 1.

[0016] FIGS. 7-9 illustrate boundaries that are displayed on a screen ofthe material handler shown in FIG. 1.

[0017] Before one embodiment of the invention is explained in detail, itis to be understood that the invention is not limited in its applicationto the details of construction and the arrangements of the componentsset forth in the following description or illustrated in the drawings.The invention is capable of other embodiments and of being practiced orbeing carried out in various ways. Also, it is understood that thephraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including” and “comprising” and variations thereof herein is meant toencompass the items listed thereafter and equivalents thereof as well asadditional items. The use of “consisting of” and variations thereofherein is meant to encompass only the items listed thereafter. The useof letters to identify elements of a method or process is simply foridentification and is not meant to indicate that the elements should beperformed in a particular order.

DETAILED DESCRIPTION

[0018]FIG. 1 illustrates a material handler 10 of the present invention.The material handler 10 includes a frame 12, a front axle 14, a rearaxle 16, front wheels 18A, 18B, and rear wheels 20A, 20B. The frame 12is supported above the ground for movement by the axles 14, 16 and thewheels 18A, 18B, 20A, 20B. The material handler 10 includes an engine(not shown) that is operably coupled to the axles 14, 16 to drive thewheels 18A, 18B, 20A, 20B. The material handler 10 includes anoperator's station 22 that is centrally located above the frame 12.

[0019] The material handler 10 includes a telescoping boom 24 that isused to lift and transport loads. The telescoping boom 24 includes arearward or lower end 26 that is coupled to the rear end of the frame 12and a forward or upper end 28 that extends toward the front end of theframe 12. The telescoping boom 24 is extendable between a retractedposition and an extended position and pivotable between a loweredposition and a raised position. The telescoping boom 24 is extended andpivoted by respective hydraulic cylinders (not shown) that arecontrolled by the operator from the operator's station 22. Thetelescoping boom 24 is equipped with a fork 30 that is insertableunderneath a load in order to raise and move the load to anotherposition. Other attachments, such as a truss boom or bucket, areinterchangeable with the fork 30.

[0020]FIGS. 2 and 3 illustrate the front axle 14 and the front wheels18A, 18B. The front axle 14 is pivotally connected to the frame 12 at apivot union 32 that divides the front axle 14 into first and secondportions 34, 36. The front axle 14 is either fixed relative to the frame12 or pivotal about a horizontal axis 38 with a controlled levelingsystem. The horizontal axis 38 extends centrally along the length of theframe 12. The controlled leveling system allows an operator tocontrollably level the frame 12 relative to the front axle 14. Thecontrolled leveling system includes a first hydraulic cylinder 40 thatis connected between the frame 12 and the first portion 34 of the frontaxle 14 and a second hydraulic cylinder 42 that is connected between theframe 12 and the second portion 36 of the front axle 14. The controlledleveling system is also operable with only a single hydraulic cylinderthat is connected between the frame 12 and the axle 14. The operatorcontrols the extension and retraction of the cylinders 40, 42 to tiltthe axle and thereby level the frame 12. The hydraulic cylinders 40, 42do not permit any free movement and only extend or retract in responseto operator commands.

[0021] The first front wheel 18A is rotatably connected to the firstportion 34 of the front axle 14 and the second front wheel 18B isrotatably connected to the second portion 36 of the front axle 14 suchthat the front wheels 18A, 18B can be driven by the engine to move theframe 12 of the material handler 10. The portions 34, 36 of the frontaxle 14 include steering assemblies 44 that allow the front wheels 18A,18B to pivot relative to the front axle 14 about respective king pins46. This configuration allows the operator to steer the front wheels18A, 18B in order to direct the motion of the material handler 10. Theking pins 46 each include an upper king pin 48 that is inserted from thetop of the steering assembly 44 and a lower king pin 48 that is insertedfrom the bottom of the steering assembly 44 and connected to the upperking pin 48.

[0022]FIGS. 4 and 5 illustrate the rear axle 16 of the material handler10. The rear axle 16 is pivotally connected to the frame 12 at a pivotunion 32 that divides the rear axle 16 into first and second portions34, 36. The rear axle 16 is freely pivotable about the horizontal axis38 or controllably fixed with an axis stabilization system 52. The axisstabilization system 52 allows the operator to prevent the rear axle 16from pivoting in one or both directions. The axis stabilization system52 includes a lockable shock absorber 54 that is connected between theframe 12 and the first portion 34 of the rear axle 16.

[0023] The lockable shock absorber 54 is freely extendable andretractable when the lockable shock absorber is in a free state suchthat the rear axle 16 is freely pivotable relative to the frame 12. Thelockable shock absorber 54 is freely extendable but locked againstretraction when the lockable shock absorber 54 is in a first fixed stateto prevent further retraction that would otherwise place the machine'scenter of gravity beyond limits in the direction of retraction. Thelockable shock absorber 54 is freely retractable but locked againstextension when the lockable shock absorber 54 is in a second fixed stateto prevent further extension that would otherwise place the machine'scenter of gravity beyond limits in the direction of extension. Thereforethe rear axle 16 is prevented from pivoting in a counterclockwise (asseen in FIG. 5) direction when the lockable shock absorber 54 is in thefirst fixed state and the rear axle 16 is prevented from pivoting in aclockwise direction when the lockable shock absorber 54 is in the secondfixed state. In addition, the rear axle 16 is prevented from anyrotation relative to the frame 12 when lockable shock absorber 54 is ina third fixed state. The lockable shock absorber 54 generate a firstfixed signal when the lockable shock absorber 54 is in the first fixedstate, a second fixed signal when the lockable shock absorber 54 is inthe second fixed state, and a third fixed signal when the lockable shockabsorber 54 is in the third fixed state.

[0024] The first rear wheel 20A is rotatably connected to the firstportion 34 of the rear axle 16 and the second rear wheel 20B isrotatably connected to the second portion 36 of the rear axle 16 suchthat the rear wheels 20A, 20B can be driven by the engine to move theframe 12 of the material handler 10. The portions 34, 36 of the rearaxle 16 include steering assemblies 44 that allow the rear wheels 20A,20B to pivot relative to the rear axle 16 the respective king pins 46.This configuration allows the operator to steer the rear wheels 20A, 20Bin order to direct the motion of the material handler 10. The materialhandler configuration described above is known to those ordinarilyskilled in the art.

[0025] As shown schematically in FIGS. 6-9, the material handler 10includes a control system 58 that determines the center of gravity ofthe material handler and a load supported by the material handler anddisplays the location of the center of gravity within a virtual plane 60that is a representation of a plane defined by the front and rear wheels18A, 18B, 20A, 20B. The plane defined by the wheels is substantiallyhorizontal when the material handler 10 is on substantially levelground. The control system 58 includes sensors 62, 64, 66, 68 thatgenerate signals which correspond to the force that the material handler10 applies to each wheel. The sensors 62, 64, 66, 68 are positioned onthe lower king pins 48 adjacent to the wheels 18A, 18B, 20A, 20B,respectively. Each sensor is a strain gage that is mounted to therespective lower king pin 48 such that when a force is applied to theadjacent wheel the strain gage is capable of generating a correspondingsignal from stresses transferred to the adjacent lower king pin 48.

[0026] The control system 58 includes a controller 70 such as amicroprocessor that receives the signals from the sensors 62, 64, 66, 68and determines the location of the center of gravity with respect to thewheels 18A, 18B, 20A, 20B based upon the relative amount of forceapplied to each wheel 18A, 18B, 20A, 20B from the frame 12. For example,if the load is distributed equally between the four wheels 18A, 18B,20A, 20B, the center of gravity would be centered between the front andrear wheels 18A, 18B, 20A, 20B and centered between the first portions34 of the axles 14, 16 and the second portions 36 of the axles 14, 16.One such commercially available microprocessor is Part No. DS-50, whichis manufactured by PAT America, Inc.

[0027] The control system 58 includes a screen 72 that is mounted in theoperator's station 22 and that displays the center of gravity with acursor 74 located on the screen 72. The cursor 74 can be any visual cuethat identifies a position. The screen 72 is preferably a thin filmelectroluminescent display that is capable of displaying a wide range ofgraphics. The screen 72 also displays the cursor 74 relative to aboundary 76 that defines a productive zone 78 in which the materialhandler 10 is stable and a non-productive zone 80 in which the materialhandler 10 is unstable, which represents a loading condition in whichthe material handler 10 is likely to tip over. The boundaries 76 areautomatically variable depending upon the state of the rear axle 16.Specifically, the boundary 76 is changed according to the signalsgenerated by the lockable shock absorber 54 and received by thecontroller 70.

[0028] FIGS. 7-9 illustrate boundaries 76 that are displayed on thescreen 72 of the control system 58. FIG. 7 illustrates the boundary 76that is displayed when the first and second lockable shock absorber 54is in the free state and the rear axle 16 is freely pivotable. Theboundary 76 is generally triangular and represents a line that connectsthe front wheels 18A, 18B and lines that converge from the front wheels18A, 18B to a point 82 located between the rear wheels 20A, 20B.

[0029]FIG. 8 illustrates the boundary 76 that is displayed when thelockable shock absorber 54 is in the first fixed state such that therear axle 16 is allowed to rotate in a first direction (e.g., in acounterclockwise direction as shown in FIG. 5) and prevented fromrotating in a second direction. The boundary 76 represents a line thatextends from the first front wheel 18A to the second front wheel 18B,from the second front wheel 18B to the second rear wheel 20B, from thesecond rear wheel 20B to the point 82 between the first and second rearwheel 20A, 20B, and from the point 82 to the first front wheel 18A.Alternatively, if the lockable shock absorber 54 is in the second fixedstate, the rear axle 16 is allowed to rotate in a second direction(e.g., in a clockwise direction as shown in FIG. 5). In this case, theboundary 76 represents a line that extends from the first front wheel18A to the second front wheel 18B, from the second front wheel 18B tothe point 82 between the first and second rear wheel 20A, 20B, from thepoint 82 to the first rear wheel 20A, and from the first rear wheel 20Ato the first front wheel 18A.

[0030]FIG. 9 illustrates the boundary 76 that is displayed when thelockable shock absorber 54 is in the third fixed state and the rear axle16 is non-pivotable relative to the frame 12. The boundary 76 isrectangular and is defined by the first front wheel 18A, the secondfront wheel 18B, the first rear wheel 20A, and the second rear wheel20B.

[0031] The location of the center of gravity changes as the loadingconditions of the material handler 10 change. Operation of the boom 24is a major factor in determining the position of the center of gravity.The center of gravity moves relative to the plane defined by the wheelbase by such actions as lifting a load with the telescoping boom 24,pivoting the boom 24, and extending the boom 24. Other factors thatdetermine the location of the center of gravity of the material handler10 are the slope and grade of the terrain, and acceleration forces fromturning, moving, and braking the material handler 10.

[0032] The controller 70 may prevent the execution of material handlerfunctions that would otherwise move the displayed center of gravity fromthe productive zone 78 into the non-productive zone 80. For example, ifthe cursor 74 is located near the right edge of the boundary 76displayed in FIG. 7 and the operator attempts to extend the telescopingboom 24 which, under normal circumstances, would potentially tip thematerial handler 10 forward, then the controller 70 prevents theextension of the telescoping boom 24 by not sending the signal from theoperator controls to the telescoping boom 24. The illustrated embodimentprevents the operations of the telescoping boom 24 if those operationswould otherwise move the center of gravity into the non-productive zone80. Other functions of the material handler 10 can be monitored in asimilar manner and such monitoring is within the scope of the presentinvention.

We claim:
 1. A material handler comprising: a frame; first and secondfront wheels rotatably coupled to the frame; first and second rearwheels rotatably coupled to the frame, the front and rear wheelssupporting the frame for movement over the ground and defining a plane;and a control system that determines the center of gravity of thecombination of the material handler and any load supported by thematerial handler and displays the location of the center of gravitywithin a virtual plane that is a representation of the plane defined bythe wheels.
 2. The material handler of claim 1, wherein the planedefined by the wheels is substantially horizontal when the materialhandler is on substantially level ground.
 3. The material handler ofclaim 1, wherein the control system includes a screen and displays thecenter of gravity with a cursor located on the screen.
 4. The materialhandler of claim 1, wherein the control system includes first, second,third, and fourth sensors that generate signals corresponding to theforce that the material handler applies to each wheel.
 5. The materialhandler of claim 4, further comprising a front axle coupled to theframe, the first front wheel being rotatably coupled to a first portionof the front axle and the second front wheel being rotatably coupled toa second portion of the front axle, and a rear axle coupled to theframe, the first rear wheel being rotatably coupled to a first portionof the rear axle and the second rear wheel being rotatably coupled to asecond portion of the rear axle, wherein the control system includes afirst sensor positioned on the front axle adjacent to the first frontwheel, a second sensor positioned on the front axle adjacent to thesecond front wheel, a third sensor positioned on the rear axle adjacentto the first rear wheel, and a fourth sensor positioned on the rear axleadjacent to the second rear wheel, and wherein the sensors generatesignals corresponding to the force that the material handler applies toeach wheel.
 6. The material handler of claim 5, wherein the front andrear axles include lower king pins located at the first portion of thefront axle, the second portion of the front axle, the first portion ofthe rear axle, and the second portion of the rear axle, and wherein thesensors are located on the lower king pins.
 7. The material handler ofclaim 6, wherein the sensors are strain gauges.
 8. The material handlerof claim 1, wherein the control system also displays the location of thecenter of gravity relative to a boundary, the boundary defining aproductive zone in which the material handler is stable and annon-productive zone in which the material handler is unstable.
 9. Thematerial handler of claim 8, further comprising a front axle coupled tothe frame, the first front wheel being rotatably coupled to a firstportion of the front axle and the second front wheel being rotatablycoupled to a second portion of the front axle, and a rear axle coupledto the frame, the first rear wheel being rotatably coupled to a firstportion of the rear axle and the second rear wheel being rotatablycoupled to a second portion of the rear axle, wherein the front axle isnon-pivotable relative to the frame, wherein the rear axle includesmultiple states, and wherein the boundary changes depending on the stateof the rear axle.
 10. The material handler of claim 9, wherein the rearaxle are is freely pivotable relative to the frame and wherein theboundary is generally triangular and represents a line that connects thefront wheels and lines that converge from the front wheels to a pointlocated between the rear wheels.
 11. The material handler of claim 9,wherein the rear axle pivotable in only one direction relative to theframe and wherein the boundary represents a line that extends from thefirst front wheel to the second front wheel, from the second front wheelto a point between the first and second rear wheel, from the point tothe second rear wheel, and from the second rear wheel to the firstwheel.
 12. The material handler of claim 9, wherein the rear axle isnon-pivotable relative to the frame and wherein the boundary representsa rectangle defined by the first front wheel, the second front wheel,the first rear wheel, and the second rear wheel.
 13. The materialhandler of claim 9, further comprising lockable shock absorber connectedto the frame and the rear axle, wherein the lockable shock absorberincludes a free state where the lockable shock absorber is freelyextendable and retractable and a first fixed state where the lockableshock absorber is prevented from retracting such that the rear axle isonly allowed to pivot in one direction, the lockable shock absorbergenerating a fixed signal when the lockable shock absorber is in thefirst fixed state.
 14. The material handler of claim 13, wherein thecontrol system receives a first fixed signal from the lockable shockabsorber and displays a boundary based on the first fixed signal fromthe lockable shock absorber.
 15. The material handler of claim 13,wherein the lockable shock absorber includes a second fixed state wherethe lockable shock absorber is prevented from retracting such that therear axle is only allowed to pivot in the opposite direction, thelockable shock absorber generating a second fixed signal when thelockable shock absorber is in the second fixed state.
 16. The materialhandler of claim 15, wherein the control system receives the fixedsignals from the lockable shock absorber and displays a boundary basedon the fixed signals from the lockable shock absorber.
 17. The materialhandler of claim 8, wherein the control system prevents the execution ofmaterial handler functions that would otherwise move the displayedcenter of gravity from the productive zone into the non-productive zone.18. The material handler of claim 17, wherein the control system allowsmaterial handler functions that move the displayed center of gravityanywhere within the productive zone.
 19. The material handler of claim18, further comprising a telescoping boom coupled to the frame andmovable between a retracted position and an extended position, andpivotable between a lowered position and a raised position, wherein thematerial handler functions include extending and pivoting the boom. 20.A method of monitoring the center of gravity of the combination of amaterial handler and any load supported by the material handler, themethod comprising: determining the center of gravity of the combinationof the material handler and the load; and displaying the location of thecenter of gravity of the combination of the material handler and theload within a virtual plane that is a representation of a plane definedby front and rear wheels.
 21. The method of claim 20, wherein displayingthe location of a center of gravity of the material handler within avirtual plane includes displaying the location of the center of gravityof the material handler within the virtual plane that is arepresentation of a substantially horizontal plane that is defined bythe front and rear wheels.
 22. The method of claim 20, whereindisplaying the location of a center of gravity of the material handlerwithin a virtual plane includes displaying the location of the center ofgravity of the material handler within the virtual plane with a cursorlocated on a screen.
 23. The method of claim 20, wherein determining thecenter of gravity includes determining the force that the materialhandler applies to a first front wheel, a second front wheel, a firstrear wheel, and a second rear wheel.
 24. The method of claim 20, whereindisplaying the location of the center of gravity includes displaying thelocation of the center of gravity relative to a boundary, the boundarydefining a productive zone in which the material handler is stable andan nonproductive zone in which the material handler is unstable.
 25. Themethod of claim 24, further comprising changing the boundary dependingon whether first and second portions of a rear axle are in a fixed statewhere the portion is non-pivotable relative to the frame or a free statewhere the portion is freely pivotable relative to the frame and theother portion of the rear axle.
 26. The method of claim 25, whereindisplaying the location of the center of gravity relative to a boundaryincludes displaying a generally triangular boundary that represents aline that connects the front wheels and lines that converge from thefront wheels to a point located between the rear wheels when the firstand second portions of the rear axle are in the free state.
 27. Themethod of claim 25, wherein displaying the location of the center ofgravity relative to a boundary includes displaying a boundary thatrepresents a line that extends from the first front wheel to the secondfront wheel, from the second front wheel to a point between the firstand second rear wheel, from the point to the second rear wheel, and fromthe second rear wheel to the first wheel when the first portion of therear axle is in the free state and the second portion of the rear axleis in the fixed state.
 28. The method of claim 25, wherein displayingthe location of the center of gravity relative to a boundary includesdisplaying a boundary that represents a rectangle that is defined by thefirst front wheel, the second front wheel, the first rear wheel, and thesecond front wheel when the first and second portions of the rear axleare in a fixed state.
 29. The method of claim 24, further comprisingpreventing the execution of material handler functions that wouldotherwise move the displayed center of gravity from the productive zoneinto the non-productive zone.
 30. The method of claim 29, furthercomprising allowing material handler functions that move the displayedcenter of gravity anywhere within the productive zone.
 31. The method ofclaim 30, further comprising providing a telescoping boom coupled to theframe and movable between a retracted position and an extended position,and pivotable between a lowered position and a raised position, whereinpreventing the execution of material handler functions includespreventing the telescoping boom from being extended and pivoted.
 32. Acontrol system for a material handler that includes a frame, first andsecond front wheels rotatably coupled to the frame, first and secondrear wheels rotatably coupled to the frame, the wheels supporting theframe for movement over the ground and defining a plane, the controlsystem comprising: four sensors, each sensor adapted to generate asignal indicative of a load applied to a respective one of the wheels ofthe material handler; a controller that determines the center of gravityof the combination of the material handler and a load supported by thematerial handler based on the signals generated by the sensors; and adisplay that displays the location of the center of gravity within avirtual plane that is a representation of the plane defined by front andrear wheels.
 33. The control system of claim 32, wherein the materialhandler includes a telescoping boom coupled to the frame and movablebetween a retracted position and an extended position, and pivotablebetween a lowered position and a raised position.